int OpenSendSock(u_int32_t addr, u_short port, unsigned char* ttl)
{
  int fd;
  struct sockaddr_in sin;

  fd = socket(AF_INET, SOCK_DGRAM, 0);
  if (fd < 0) {
    perror("socket");
    exit(1);
  }
  nonblock(fd);
  memset((char *)&sin, 0, sizeof(sin));
  sin.sin_family = AF_INET;
  sin.sin_port = port;
  sin.sin_addr.s_addr = addr;
  if (connect(fd, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
    perror("connect");
    exit(1);
  }
  if (IN_CLASSD(ntohl(addr))) {
#ifdef IP_ADD_MEMBERSHIP
    if (setsockopt(fd, IPPROTO_IP, IP_MULTICAST_TTL,
		   &ttl, sizeof(ttl)) < 0) {
      perror("IP_MULTICAST_TTL");
      exit(1);
    }
#else
    fprintf(stderr, "\
not compiled with support for IP multicast\n\
you must specify a unicast destination\n");
    exit(1);
#endif
  }
  return (fd);
}
int OpenRcvSock(u_int32_t addr, u_short port,
		const struct sockaddr_in* local)
{
  int fd;
  int on = 1;
  struct sockaddr_in sin; 
  struct ip_mreq mr;
  fd = socket(AF_INET, SOCK_DGRAM, 0);

  if (fd < 0) {
    perror("socket");
    exit(1);
  }
  nonblock(fd);
 
  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *)&on,
		 sizeof(on)) < 0) {
    perror("SO_REUSEADDR");
  }

#ifdef SO_REUSEPORT
  on = 1;
  if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, (char *)&on,
		 sizeof(on)) < 0) {
    perror("SO_REUSEPORT");
    exit(1);
  }
#endif

  memset((char *)&sin, 0, sizeof(sin));
  sin.sin_family = AF_INET;
  sin.sin_port = port;

#ifdef IP_ADD_MEMBERSHIP
  if (IN_CLASSD(ntohl(addr))) {
    /*
     * Try to bind the multicast address as the socket
     * dest address.  On many systems this won't work
     * so fall back to a destination of INADDR_ANY if
     * the first bind fails.
     */
    
    sin.sin_addr.s_addr = addr;
    if (bind(fd, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
      sin.sin_addr.s_addr = INADDR_ANY;
      if (bind(fd, (struct sockaddr*)&sin, sizeof(sin)) < 0) {
	perror("bind");
	exit(1);
      }
    }
    
    /* 
     * XXX This is bogus multicast setup that really
     * shouldn't have to be done (group membership should be
     * implicit in the IP class D address, route should contain
     * ttl & no loopback flag, etc.).  Steve Deering has promised
     * to fix this for the 4.4bsd release.  We're all waiting
     * with bated breath.
     */
   
    mr.imr_multiaddr.s_addr = addr;
    mr.imr_interface.s_addr = INADDR_ANY;
    if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, 
		   (char *)&mr, sizeof(mr)) < 0) {
      perror("IP_ADD_MEMBERSHIP");
      exit(1);
    }
  } else
#endif
    {
      sin.sin_addr.s_addr = local->sin_addr.s_addr;
  
      if (bind(fd, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
	perror("bind");
	exit(1);
      }
      sin.sin_port = 0;
      sin.sin_addr.s_addr = addr;
      connect(fd, (struct sockaddr *)&sin, sizeof(sin));
      return (fd);
    }
}